Antivirals

There are currently four antiviral agents on the market for preventing or treating influenza. To decrease the opportunity for resistance to these medications, they are primarily used in individuals who are at high risk for complications and their close contacts. These medications include:

• amantadine (Symmetrel)
• rimantadine (Flumadine)
• oseltamivir (Tamiflu)
• zanamivir (Relenza)

Amantadine and rimantadine

• are effective against susceptible influenza A viruses
• 92% of H3N2 Influenza A Virus are already resistant to the medication. Because of this it is recommended that these medications not be used for prevention or treatment of influenza unless special circumstances warrant, such as failure to respond to all other treatments.

Oseltamivir (Tamiflu)

• is effective for prevention and treatment of influenza caused by the A and B virus
• is considered to be 80 to 90% effective when started within 36 to 48 hours of exposure to the virus and taken for a period of 5 days
• is available in capsule and liquid form
• is approved for adults and children over one year of age
• is preferred in nursing home patients due to the risk of bronchospasm with zanamivir
• side effects, which include nausea and vomiting, may be reduced by taking the medication with a light snack
• no drug interactions have been reported

Zanamivir (Relenza)

• is effective for prevention and treatment of influenza caused by the A and B virus
• is considered to be 80-90% effective when started within 36 48 hours of exposure to the virus and taken for 5 days
• is available in aerosol form for oral inhalation
• is approved for treatment in adults and children 7 years of age and older
• is approved for prevention in adults and children 5 years of age and older
• is not recommended for patients with asthma, chronic obstructive lung disease, or who may be considered to be at risk for bronchospasm
• side effects include headache, throat discomfort, nasal symptoms, cough, and bronchospasm
• no drug interactions have been reported

When are antivirals used for prevention of influenza?

Antivirals are primarily used for influenza prevention when:

• there has been an influenza outbreak affecting nursing homes and other long term care facilities
• patients who are at high risk for serious complications have come into contact with influenza
• people in close contact of high risk patients have come into contact with influenza

Are antivirals used in vaccinated individuals?

Antivirals may be used in individuals who have been vaccinated if:

• they are at high risk for complications
• they are in close contact with high risk individuals and have come into contact with the influenza virus before the vaccine has had an opportunity to be effective.
• they are expected to have an impaired immune response to the vaccine
• they are at high risk for complications and the influenza outbreak is caused by a virus not found in the vaccine
• if they are in close contact with high risk individuals and the influenza outbreak is caused by a virus not found in the vaccine